What is the role of semicolons in Bash?

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The semicolon, which plays a special role in shell, is similar to pressing enter in PS1. It is mainly used in the following scenarios and usually brings great convenience.

1 multi-line command, single-line input.

(2) use with sleep.

3 if there are a series of commands, each command needs to be executed for a long time, you can enter it at once without waiting for the first command to finish executing before running the second command.

Example:

1 multi-line command, single-line input

Command 1; command 2; command 3

Echo'I am here'; echo'I am not here'; echo'in fact, I am here today

2 used with sleep, similar to 5 4 3 2 1 intermediate break

Echo 'CTRL C to cacel'; sleep 10; echo' Done'

More than 3 commands that take a long time are entered at one time and executed slowly.

Sleep 500; sleep 500; sleep 500

Echo $$; echo $$; echo $$

But why on earth does the semicolon play this role? That is, why is it executed sequentially instead of concurrently? Look at this command:

Echo $$; echo $$; echo $$

21304

21304

21304

You will find that the output is a PID, that is, all three commands are executed in the same process. -sequential execution.

That is, the same sentence, the semicolon, which is considered the end of a command in shell, is similar to typing a command in shell and pressing enter.

Ps-ef | grep pts/0

Root 21302 1582 0 Dec26? 00:00:00 sshd: root@pts/0

Root 21304 21302 0 Dec26 pts/0 00:00:00-bash

Root 28290 21304 0 09:55 pts/0 00:00:00 ps-ef

Root 28291 21304 0 09:55 pts/0 00:00:00 grep pts/0

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